A conventional configuration for a deposition reactor is an open-ended, substantially tubular-shaped chamber, a portion of which is mounted within a furnace or heating means. In the deposition process, a substrate is placed in a heated portion of the reactor and appropriate reactant gases are introduced such that they pass over the substrate. For example, to deposit an epitaxial layer of GaAs on a GaAs substrate, the reactant gases contain GaCl and AsH.sub.3 and the substrate is heated to about 700.degree. C. Additionally, controlled amounts of impurities may be introduced during the deposition, for example, so as to form N or P doping in the epitaxial film. As more and more III-V compounds are used for high performance devices made by epitaxial vapor deposition, the adverse sensitivity to contaminants present in the conventional reactor tube is critically important.
The contaminants are derived from materials such as quartz of which the reactor chambers are made. Quartz contains residues of water which decompose into oxygen and hydrogen, the oxygen doping the deposited layer unfavorably. Moreover, iron, for example, and other contaminants in trace quantities, may be present in the quartz which can react with the chlorides to form metallic chloride vapors which mix with the deposition material adversely. Moreover, silicon from the quartz can function as a contaminant when it is in a non-silicon containing layer. For a more detailed description of the contaminating effects of materials such as quartz, see the following articles: "Effects Of The AsCl.sub.3 Mole Fraction On The Incorporation of Germanium, Silicon, Selenium, And Sulfur Into Vapor Grown Epitaxial Layers of GaAs, "by J. V. DiLorenzo and G. E. Moore, Jr., J. Electrochem. Soc.: Solid State Science, Vol. 118, No. 11, November 1971 and "Vapor Growth Of Epitaxial GaAs: A Summary Of Parameters Which Influence The Purity And Morphology Of Epitaxial Layers, " by J. V. DiLorenzo, Journal of Crystal Growth 17 (1972).
It is clear there is a need in the art for a reactor that provides a deposition environment that is substantially free, if not totally free, of contaminants that evolve from conventional reactor apparatus.